Diode detector circuit



1 l l i l l I i l l l l l i i l l l l NVENTOR. THEODORE G. ANDERSON 8%/ T. G. ANDERSON DIODE DETECTOR CIRCUIT Flled June l2, 1945 h g, ama

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Patented Mar. 9, 1948 DIODE DETECTOR CIRCUIT Theodore G. Anderson, Kennett Square, Pa., as-

sgnor by mesne assignments, to Hazeltine Research, Inc., Chicago, Ill., a corporation of Illinois Application June 12, 1945, Serial No. 599,002

(Cl. Z50-27) 7 Claims.

This invention relates to detector arrangements for wave-signal translating systems. More particularly the invention is directed to detectors of the diode type arranged to supply modulation components from a modulated carrier wave to a translating stage in a Wave-signal receiving set.

Wave-signal receivers, especially those used in commercial broadcast reception, are often provided With a diode detector arrangement for deriving the modulation components from a modulated-carrier wave signal. In the usual case, the output circuit of the diode detector comprises a simple time-constant circuit for supplying an audio amplifier with the desired detected components. This type of load circuit causes a loading effect on the preceding stage of the receiver and may be responsible for an undesirable amount of distortion in the detected signal output.

It is an object of the present invention, therefore, to provide a detector arrangement which avoids the aforementioned limitation of the prior arrangements.

Another object of the invention is to provide an improved diode detector arrangement in which a very small amount of power is required from the detector input circuit.

Another object of the invention is to provide an improved diode detector arrangement in which the detector output circuit is made up of components having comparatively low impedance values while at the same time presenting a high effective impedance.

Itis a specific object of the invention to provide a diode detector arrangement which employs a cathode-follower triode to apply a regenerative voltage feedback to the diode output circuit while at the same time transmitting modulation components to an audio-frequency amplifier.

In accordance with the invention a detector arrangement for a wave-signal translating system comprises a two-element rectifier, or'diode, and means for applying to the rectifier an input signal having desired modulation components. A load circuit is coupled to the rectier and includes an impedance for deriving the desired modulation components. The detector arrangement has a modulation-signal translating circuit for the rectiiier including a signal-translating stage having input and output circuits. A means, including a first portion of the load impedance, is provided for applying the modulation components to the input circuit of the stage. 'I'he detector arrangement also contains means, comprising a second portion of the load impedance, for applying the. translated modulation components in the output circuit in a regenerative sense to the load circuit of the rectier.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

The single figure of the accompanying drawing is a circuit diagram, partly schematic, of a complete Wave-signal receiver of the superheterodyne type embodying one form of the invention.

Referring now to the drawing in detail, the receiver there represented includes an antennaground system I0 and II to which are connected in cascade and in the order named, a radio-irequency amplier I2, an oscillator-modulator or frequency changer I3, an intermediate-frequency amplifier I4, a detector and automatic volume control (A. V. C.) arrangement I5 hereinafter described in more detail, and an audio-frequency amplifier I5, to which is coupled a sound-signal reproducer or loud-Speaker I1. A transformerrectifier type of voltage supply I8 is connected with unit I5 in a fashion to be pointed out hereinafter. The stages or units I2, I3, I4, I6 and I'I may all be of conventional Well-known construction so that detailed illustrations and descriptions thereof are unnecessary herein.

Considering briefly the operation of the receiver as a whole, and neglecting for the moment the operation of the present invention, a signal received by the antenna-ground system I0, Il is selected and amplified in radio-frequency amplifier I2 and applied to oscillator-modulator I3 wherein it is converted into an intermediatefrequency signal. The intermediate-frequency signal is amplied in amplifier I4 and supplied to unit I5 wherein the modulation components of the received signal are derived in a manner vto be described presently. The modulation or arrangement I5 and applied over a conductor 2!) to one or more of units I2, I3 and I4 to control the gain of these units in order to maintain the signal input to the detector unit I5 within a relatively narrow range for a wide range of received signal intensities.

Referring now more particularly to the detector arrangement I5 embodying the present invention, this arrangement comprises a two-element rectier, specically a diode vacuum tube 2| having a cathode .and an anode. A means is provided for applying to the rectifier 2| an input signal which has the desired modulation components. This means includes the secondary portion 22 of a double-tuned transformer 22, 23. The primary winding of the transformer is connected to the output terminals of the intermediate-frequency amplifier .I4 and forms the usual transformer coupling between the intermediate-frequency amplifier and detector stages. A load circuit i-s coupled to the rectier 2| and includes an impedance for deriving the desired modulation components. Specifically, the load impedance is a time-constant; circuit, the resistance component of which includes resistors 26, 25- and the portion of resistor 36 between a tap thereon and a ground connection at one end thereof. The condenser component of the time-constant circuit comprises condensers 28 and 3| arranged in series with each other but effectively connected in parallel to the three resistors.

A modulation-signal translating circuit is provided for the rectifier and includes a signaltranslating stage having input and output circuits. This stage comprises a triode tube 24 and the input circuit thereof includes the control electrode and cathode of the tube while the output circuit comprises the above-mentioned portion of resistor 36, resistor 25 and a resistor 32 connected between resistor 25 and the cathode of the tube.

A means4 is included in the :arrangement under consideration by which a '.rst portion of the loa-d impedance cf rectifier 2| is utilized to apply the modulation components to the input circuit of the stage including tube 24. This last-named means includes a provision for applying the Voltage across resistor 26 to the input electrodes of tube 24 through a resistant-capacity filter comprising a series resistor 21,'condenser 28 and a. condenser 30 arranged in parallel connection.

A means is provided for applying the translated modulated components in the, output circuit of the stage 24 in` a. regenerative sense to the load circuit of the rectier. This means comprises a second portion of the load impedance of rectifier 2| and includes resistor 25` and Vthe above-mentioned portion of resistor 36 which are common to the load circuit of detector 2| and the output circuit of the stage which includesl the triode 24.

Resistor 25 is tapped at an appropriate point to supply a voltage for automatic volume control (A. V. C.). Connection is made by means of conductors 33 and 20 and the voltage may be applied to. any one or all of the receiver components I2, I3 and I4. A lter comprising a resistor 34 and a condenser 3 5 is connected. in the A. V.,C', line between conductors 33 and 20 to filter out vaudio-frequency components.

The power supply unit. I8 is of conventional design except for the resistor 36 which isY inserted in the negative-potential side of the full--wavev rectifier circuit.

Since the entire output circuit impedance of tube 24 is connected between the cathode of this tube and ground, a direct connection 31 is made from the anode to the positive-potential terminal of power supply I8.

A means for supplying the desired modulation components to the audio-frequency amplifier I6 comprises a blocking condenser 38 and a volumecontrol potential divider 4&1. The volume-control unit may be the usual voltage divider as indicated in the figure or anyother circuit means adapted to perform this function.

In considering the operation of the diode detector arrangement I5, let it be assumed initially that no wave signal is received at the antenna. For the assumed condition no input signal is applied to tube 2| which is therefore in its quiescent state. Tube 24 also has no input signal and is quiescent. The values of the circuit elements associated with these tubes and the potentials supplied thereto are selected to establish predetermined values of potential so that the A. V. C. line 2f) is at the proper potential for the normal operation of stages I2, I3 and I4 and the potential drop across resistor 36 is adjustably set so as to balance the potential drop across resistor 25 and keep the anode of diode 2| at ground potential.

When a received signal is intercepted by antenna system I0, II and translated through the receiver it is :applied to the input circuit of unit I5 as an intermediate-frequency signal including the desired modulation components. Signals impressed upon the diode 2| by the input circuit 22 are rectied by the tubey due to its unilateral conductiwty characteristic. The rectified pulses then ow through the load circuit of the diode which includes resistor 26, resistor 25 and part of resistor 36. In parallel with the resistive parts of the load circuit are two condensers 28 and 3| which are charged by the pulses, the magnitude of the charge being proportional to the modulation components of the carrier wave. The resulting voltage across resistor 2S is applied to the control electrode of tube 24 through resistor 2'I and causes variations in the anode-cathode current which flows through the output circuit of this tube.

It is at lonce evident that resistor 25 and part lof resistor 36 are common to the load circuit of diode 2| and the output circuit of triode 24 and since the triode receives. the signal from a part of the diode load circuit, the common circuit elements constitute 4a feed-back'. arrangement. Thus when a signal is applied to the rectifier 2 I, current flows in its load circuit which results in a potential drop across resistor 25 in such manner that the cathode side thereof becomes more negative. A portion of the detected signal is applied to tube 24 through its input circuit to cause the control electrode to become more negative, decrease the flow of current in the anode-cathode circuit and produce a potential variation in the same sense in resistor 25. Therefore, the feedback action is regenerative and the main result of such action is to lower the current flow in the diode output circuit, thus increasing its effective impedance.

Flor optimum operation, the regenerative voltage may vary from a value of half the voltage supplied by the detector output circuit to the tube 24 to a value only slightly less than the supplied voltage.

A regenerative feed-back circuit arrangement using a cathode-follower arrangement cannot return to a supply circuit more voltage than the circuit originates. Hence, there is no danger of overcompensation. If the feed-back voltage is 95. per cent. of the supply voltage, the increase in effective impedance of the diode 2 I is the ratio of unity to the difference between unity and .95 or twenty times.

The achieved result of increasing the effective impedanceby a factor of twenty is the lowering of the current drain in the input circuit to onetwentieth of its usual value.

Derivation of the desired modulation compo- 5. nents for subsequent amplification byfan audiofrequency amplifier may be accomplished by coupling across the entire output circuit of tube 24 specically, by connecting to the cathode and ground. The condenser 38 is utilized to block out the direct current components.

In the above disclosure the rectier unit has been described as a two-element diode tube, having an anode and a cathode. It is possible to substituteother rectifier units instead of the diode, such as a crystal detector, and attain-the same result. Also, the rectifier unit 2l and the triode unit 24 may be in the same envelope, an example being tube type 12A7 with the pentode part of the tube connected as a triode. Types GF6-G and GCS-G may also be used with one of the triode units connected as a diode.

As illustrative of a speciiic application of the invention, the following circuit constants are given for one embodiment of the detector arrangement.

Diode detector tube 2L- Type 6H6 Triode amplifier tube 24- Type 6J5 Resistor 25 10,000 ohms Resistor 20 100,000 ohms Resistor 21 100,000 ohms Resistor 32 1,000 ohms Resistor 34 500,000 ohms Resistor 40 500,000 ohms Condensers 28 and 3ii 100 micromicrofarads Condenser 3| 1,000 micromicrofarads Condenser 35 5 microfarads Condenser 38 1 microfarad While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A detector arrangement for a wave-signal translating system comprising, a two-element rectifier, means for applying to said rectifier an input signal having desired modulation components, a load circuit coupled to said rectifier including an impedance for deriving said desired modulation components, a modulation-signal translating circuit for said rectifier including a signal-translating stage having input and output circuits, means including a iirst portion of said load impedance for applying said modulation components to said input circuit of said stage, and means comprising a second portion of said load impedance for applying the translated modulation components in said output circuit of said stage in a regenerative sense to said load circuit of said rectifier.

2. A detector arrangement for a wave-signal translating system comprising, a two-element rectifier, means for applying to said rectifier an input signal having desired modulation components, a load circuit coupled to said rectier including an impedance for deriving said desired modulation components, a modulation-signal translating circuit for saidV rectiiier including a signal-translating stage having input and output circuits, means including a first portion of said load impedance for applying said modulation components to said input circuit of said stage, and means comprising a second portion of said load impedance for applying the translated modulation components in said output circuit of said stage in a'regenerative sense to said load circuit of said rectifier, said-rst portion of said load impedance being so proportioned with respect to said second portion that the eiectiv'e rectifier load impedance is at least twice the value of said load impedance.

3. A detector arrangement for la wave-signal translating system comprising, a two-element rectier, means for applying to' said rectifier an input signal having desired modulation components, a load circuit coupled to said rectifier including an impedance for deriving said desired modulation components, a modulation-signal translating circuit for said rectifier including a signal-translating stage having input and output circuits, means including a first portion of said load impedance for applying said modulation components to said input circuit of said stage with a given intensity, and means comprising a second portion of said load impedance for applying the translated modulation components in said output circuit of said stage in a regenerative sense to said load circuit of said rectier but with an intensity lat least equal to one-half of said given intensity. 4. A detector arrangement for a wave-signal translating system comprising, a two-element rectiner, means for applying to said rectifier an input signal having desired modulation components, a load circuit coupled to said rectiiier including an impedance for deriving said desired modulation components, a modulation-signal translating circuit for said rectiiier including lan electrondischarge device having input and output circuits, means included in said load circuit for applying said modulation components to said input circuit of said electron-discharge device, and means common to said input and output circuits of said electron-discharge device for applying the translated modulation components in said output circuit of said electron-discharge device in a regenerative sense to said load circuit of said rectier. 5. A detector arrangement for a wave-signal translating system comprising, a two-element rectifier, means for applying to said rectiiier an input signal having desired modulation components, a load circuit coupled to said rectifier including an impedance for deriving said desired modulation components, a modulation-signal translating circuit for said rectiiier including .a signal-translating stage having input and output circuits, means included in said load circuit for applying said modulation components to said input circuit of said stage with la given intensity,

and means common to said input and output circuits of said electron-discharge device for applying the translated modulation components in said output circuit of said stage in a regenerative sense to said load circuit of said rectifier but with lan intensity slightly less than said given intensity.

6. In a wave-signal receiver, a detector arrangement comprising, a two-element rectiiier, means for applying to said rectier yan input signal having desired modulation components, a load circuit coupled to said rectiiier including an impedance for deriving said desired modulation components, a modulation-signal translating circuit for said rectifier including a signal-translating stage having input and output circuits, means included in said load circuit for applying said modulation components to said input circuit of said stage, means common to said input and out- 7... in said output circuit of saidstage in a regenerative sense to said load circuit of said rectier, and means' for deriving a control voltage for automatic volume control having an amplitude characteristic determined by the intensity of said in- 8. cuit for said rectifier including a signal-translating stage having input and output circuits. means included in said load circuit for applying said 'modulation components to said input circuit of said stage, means for applying the translated modulation components in said output circuit of said stage in a. regenerative sense to said load circuit of said recti-er. and means for deriving the translated modulation components from the output circuit of said stage and applying said modulation components to an audio amplifier.

THEODORE G. ANDERSON. 

